A vehicle-mounted emergency report device mounted on a vehicle has a backup battery including a rechargeable battery such as a lithium ion battery or the like. The vehicle-mounted emergency report device can operate using the backup battery when a vehicle battery is damaged due to a traffic accident or the like. When the backup battery is exhausted during an emergency report operation such as using the backup battery for a voice call, the emergency report operation will be interrupted suddenly. To avoid such a situation, a voltage of the backup battery is detected and battery exhaustion is warned beforehand when the voltage detected drops below a predetermined reference voltage. Since the backup battery has a property that a discharge performance decreases in a low-temperature environment, the battery exhaustion of the backup battery is likely to occur in the low-temperature environment.